Vol. 61 No. 9 • JOM 21 www.tms.org/jom.html Overview Biomedical Materials and Devices The selection criteria for biomateri- als include the material’s properties and biocompatibility, and the ability to fab- ricate the desired shapes. Bulk metallic glasses (BMGs) are relative newcomers in the field of biomaterials but they ex- hibit an excellent combination of prop- erties and processing capabilities de- sired for versatile implant applications. To further evaluate the suitability of BMGs for biomedical applications, we analyzed the biological responses they elicited in vitro and in vivo. The BMGs promoted cell adhesion and growth in vitro and induced improved foreign body responses in vivo suggesting their potential use as biomaterials. Because of the BMGs’ flexible chemistry, atomic structure, and surface topography, they offer a unique opportunity to fabricate complex implants and devices with a desirable biological response from a material with superior properties over currently used metallic biomaterials. INTRODUCTION The availability and suitability of traditional materials for bio-prosthetic elements are limited. As a result, sig- nificant interest has been drawn to de- veloping synthetic materials, which promise asymptomatic, long-term use within the body. Material choice is defined by the function of the implant and the material’s compatibility with the body’s internal environment. Fur- thermore, the selection of an implant material also depends on its ability to be fabricated into a desired shape. Cur- rent biomaterials include a wide range of natural and manufactured materials such as ceramics, metals, and both syn- thetic polymers and biopolymers. Each type of material has its own positive aspects that are particularly suited for specific applications. Bulk Metallic Glasses for Biomedical Applications Jan Schroers, Golden Kumar, Thomas M. Hodges, Stephen Chan, and Themis R. Kyriakides bearing large loads without excessive deformation and permanent dimension- al changes. Metallic implants are main- ly used as prostheses to replace a miss- ing body part and as fixation devices to stabilize bones and tissues during the healing process. Metals and alloys that are successfully used as biomaterials include steels, titanium-based alloys, Ni-Ti (shape memory alloy), cobalt- based alloys, and precious metal alloys. However, usage of metallic implant ma- terials is limited by complex fabrication methods, which restrict design options, and also by their reduced long-term sta- bility in corrosive environments. There- fore, the vast majority of bioengineer- ing applications would benefit from the availability of a biomaterial with high corrosion and wear resistance, high strength and elasticity, and the ability to be net-shaped into intricate geometries. BULK METALLIC GLASSES Bulk metallic glasses (BMGs) are metallic alloys which possess a particu- lar ease to avoid crystallization during solidification and thereby vitrify at low cooling rates. Bulk metallic glasses have attracted much attention due to their remarkable properties like high strength, elasticity, corrosion resis- tance, and unique processing capabili- ties. 2–5 During the past two decades, a wide range of BMG-forming alloys has been developed, including Zr-, 6–8 Fe-, 9,10 Cu-, 11 Ni-, 12 Ti-, 13 Mg-, 14 Pd-, 15 Au-, 16 and Pt-based. 17 The unusual properties of BMGs are to a large extent a con- sequence of their amorphous structure. The absence of dislocations and asso- ciated slip-planes in BMGs results in a very high strength and elasticity close to the theoretical limit. For example, a typical zirconium-based BMG yields at 2,000 MPa with an elastic strain of How would you… …describe the overall significance of this paper? This article evaluates how bulk metallic glasses (BMGs), a new material class of structural metals with outstanding mechanical properties, can be used in biomedical implants and devices. The evaluation includes the introduction of recently developed processing methods which can be utilized to precision net-shape complex geometries. …describe this work to a materials science and engineering professional with no experience in your technical specialty? The absence of grain boundaries, dislocation, and associated slip planes results in BMGs with unusual properties. Their high strength and elasticity, exceeding that of currently used biomaterials, together with good wear and corrosion resistance are attractive properties as a biomaterial. Most unique is the processability of BMGs. They can be thermoplastically formed, similar to plastics, which permits precision net-shaping of complex geometries. This, together with biocompatibility tests on some BMGs propose a wide range of applications of BMG as biomedical implants and devices. …describe this work to a layperson? Bulk metallic glass, a novel material with amorphous structure which is a high strength metal that can be formed like a plastic, is evaluated for biomedical implants and devices. Biocompatibility tests have revealed that some BMGs can be used in the human body. The use of metals in biomedical ap- plications dates back to the 16th centu- ry, when Petronius used gold plates for the repair of cleft palates. 1 A high elas- tic modulus and yield strength coupled with ductility make metals suitable for